Previous research has suggested a relationship between human psychopathology and levels of platelet MAO activity. Preliminary studies of variability in mouse MAO with age and sex are underway. The relationships between brain, liver and platelet MAO activity are also being investigated. Suggestions that MAO activity is related to general motor activity are being studied in genetically heterogeneous mice measuring activity in home cages with animex monitors. No research results are available at this writing. Normal social interactions in small groups of mice have been and are being observed. We are attempting to develop new behavioral tests in a social situation for the assessment of drug response. We are particularly interested in developing an appropriate test for the effects of LSD, amphetamines, phenothiazines and MAO inhibitors on mouse behavior.